Color filter arrays for image sensors

ABSTRACT

Methods, systems, apparatus, including computer-readable media storing executable instructions, for color filter arrays for image sensors. In some implementations, an imaging device includes a color filter array arranged to filter incident light. The color filter array has a repeating pattern of color filter elements. The color filter elements include yellow filter elements, green filter elements, and blue filter elements. The imaging device includes an image sensor having photosensitive regions corresponding to the color filter elements. The photosensitive regions are configured to respectively generate electrical signals indicative of intensity of the color-filtered light at the photosensitive regions. The imaging device includes one or more processors configured to generate color image data based on the electrical signals from the photosensitive regions.

BACKGROUND

Many image sensors use a color filter array, such as a Bayer filterarray, to distinguish between different wavelengths of light incident onthe sensor. For example, a Bayer filter uses a filter pattern that is50% green, 25% red, and 25% blue to allow the intensities of green, red,and blue light to be separately at adjacent sub-pixel photosites.

SUMMARY

In some implementations, a color filter array for an image sensorincludes an array of sub-pixel filter elements that respectively passblue, green, and yellow light. This arrangement can improve colorsensitivity and improve image noise characteristics relative totraditional Bayer color filter arrays. For example, sensitivity to redand green light can be improved using yellow-filtered regions that passboth red and green light. With the yellow light passing elements of thefilter, each pixel of the color filter array can pass more total lightthan a Bayer color filtered pixel, resulting in lower noise and/orhigher resolution. This improvement can be achieved while retaining theability to extract red, green, and blue colors, since the intensity ofred light can be inferred by subtracting the measured green lightintensity from the measured yellow light intensity.

In one general aspect, an imaging device includes: a color filter arrayarranged to filter incident light, the color filter array having arepeating pattern of color filter elements, the color filter elementsincluding yellow filter elements, green filter elements, and blue filterelements; an image sensor having photosensitive regions corresponding tothe color filter elements, the photosensitive regions being configuredto respectively generate electrical signals indicative of intensity ofthe color-filtered light at the photosensitive regions; and a processorconfigured to generate color image data based on the electrical signalsfrom the photosensitive regions.

Implementations may include one or more of the following features. Forexample, in some implementations, green light is substantiallytransmitted by 75% of the color filter elements.

In some implementations, the ratio of yellow filter elements to greenfilter elements to blue filter elements is 2:1:1.

In some implementations, the one or more processors are configured toprovide image data indicating an array of pixels, wherein each pixel isbased on electrical signals from at least one photosensitive regioncorresponding to a yellow color filter element, at least onephotosensitive region corresponding to a green color filter element, andat least one photosensitive region corresponding to a blue color filterelement.

In some implementations, the color filter elements do not include anyred color filter elements or magenta color filter elements.

In some implementations, an area of the color filter array that iscomprised of yellow filter elements is at least 50% of the averageper-pixel color-filtered area of the color filter array.

In some implementations, 75% of the color filter elements substantiallytransmit green light, and only 25% of the color filter elements filterincident light to substantially transmit only green light.

In some implementations, 50% of the color filter elements substantiallytransmit red light, and none of the color filter elements filterincident light to substantially transmit only red light.

In some implementations, the repeating pattern comprises a grid with arepeating 2 by 2 pattern of color filter elements, and wherein eachpixel of image data output by the imaging device is based on electricalsignals from four photosensitive regions respectively filtered by fourcolor filter elements, the four color filter elements including twoyellow filter elements, one blue filter element, and one green filterelement.

In some implementations, the two yellow filter elements are arrangeddiagonally across from each other in the grid, and the blue filterelement and the green filter element are arranged diagonally across fromeach other in the grid.

In some implementations, the one or more processors are configured toprovide image data having a color gamut that includes at least the sRGBcolor space or the Adobe RGB color space.

In some implementations, the one or more processors are configured todetermine a red intensity for pixels of the image data by subtracting agreen intensity from a yellow intensity.

In some implementations, the one or more processors are configured toprovide the image data in values for a blue, yellow, and green colorspace or an LMS color space.

In some implementations, the one or more processors are configured togenerate a compressed version of the image data that has a compressedform of data representing intensities of blue, yellow, and green colorchannels.

In some implementations, the color filter array comprises wherein therepeating pattern comprises a grid with a repeating 4 by 4 pattern ofcolor filter elements.

In some implementations, the color filter array comprises clear elementsin the repeating pattern, the clear elements being configured to passwhite light to corresponding photosensitive regions of the image sensor.

In some implementations, the image sensor is a complementarymetal-oxide-semiconductor (CMOS) sensor.

In some implementations, the image sensor is a charge-coupled device(CCD) sensor.

The details of one or more embodiments of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram that illustrates an example of a pixel of a Bayerfilter array.

FIG. 1B is a diagram that illustrates an example of a pixel of anenhanced color filter array.

FIG. 2A illustrates a graph of example filter response characteristicsfor elements of a Bayer color filter array.

FIG. 2B illustrates a graph of example filter response characteristicsfor an enhanced color filter array.

FIG. 3 illustrates an example of an imaging device using an enhancedcolor filter array.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1A is a diagram that illustrates an example of a pixel 100 of aBayer filter array. The pattern of the pixel 100 can be repeated to forma mosaic. The pixel 100 includes four filter elements arranged in agrid. Two filter elements pass green light, one passes red light, andone passes blue light. Accordingly, of the incident light to the pixel100, 50% of the area substantially transmits green light, 25% of thearea substantially transmits red light, and 25% of the areasubstantially transmits blue light.

FIG. 1B is a diagram that illustrates an example of a pixel 110 of anenhanced color filter array. The pattern of the pixel 110 can berepeated to form a mosaic. Like the pixel 100 of the Bayer filter, thepixel 110 includes four filter elements arranged in a grid. However, thepixel 110 includes a different set of filter elements. Two filterelements pass yellow light (e.g., substantially transmitting red andgreen light while substantially blocking blue light), one passes greenlight (e.g., substantially transmitting green light while substantiallyblocking red and blue light), and one passes blue light (e.g.,substantially transmitting blue light while substantially blocking greenand red light). As a result, of the incident light to the pixel 110, 75%of the area substantially transmits green light, 50% of the areasubstantially transmits red light, and 25% of the area substantiallytransmits blue light.

The percentages noted above are based on the area of the filter arraythat is designed to transmit light of the different colors. Actualtransmission characteristics (e.g., absolute transmission levels) willvary based on the materials of the filters. For example, a filterdesigned to transmit a color of light may substantially transmit lightof that color, e.g., transmitting that color of light more than othercolors, but may still attenuate that color to a degree, e.g., due to thenon-ideal an potentially non-linear response of the filter materials. Inother words, a color filter element can substantially transmit a colorof light even though the response of the filter even at peaktransmission wavelength is significantly less than 100%. Thetransmission efficiency of a filter may vary significantly from onedevice to another, and for filter elements for different colors. In somecases, the transmission efficiency for a transmitted color may be in therange of 20-70% for the transmitted color. Even so, the filter elementmay transmit the designated color more strongly than other colors.Similarly, a filter element for a particular color can substantiallyblock light of other colors even though the filter transmits some lightof the other colors. For photography and other imaging applications, thecolor filters for different colors have responses that overlap along therange of visible wavelengths, as shown in FIGS. 2A and 2B. The extent ofoverlap can be more or less than what is shown in FIGS. 2A and 2B.

Despite the overlap along some or all of the visible spectrum, a colorfilter is considered to substantially transmit or substantially blockcolors of light based on the relative responses of the filter elements.For example, although red and green filter elements may each respond toa degree to both red and green light, the red filter element transmits agreater amount of incident red light than green light, and the greenfilter element transmits a greater amount of incident green light thanred light. Generally, at a key wavelength for a color filter, e.g.,approximately 450 nm for blue, approximately 540 nm for green, andapproximately 650 nm for red, the response for the color substantiallypassed by the filter is much more than the response for colorssubstantially blocked by the filter. The key wavelength may be the peaktransmission wavelength for the color filter element, but is notrequired to be. At the key wavelengths, the difference in filterresponse for a filter element that substantially transmits a color oflight can be much more than (e.g., twice, three times, five times, 10times, or more) the filter response for the filter elements thatsubstantially block that color of light. Similarly, this relationshipcan also exist for a color filter for the key wavelengths for the colorsthe filter substantially transmits and the colors the filtersubstantially blocks. For example, a green color filter's response at540 nm can be twice, three times, 5 times, or ten times the response ofthe filter at 650 nm and at 450 nm. In general, blue filter elementsrespond most strongly to light in the range of approximately 400-500 nmand the key wavelength for blue light is in that range; green filterelements respond most strongly to light in the range of approximately500-570 nm and the key wavelength for green is in that range; and redfilter elements respond most strongly to light in the range ofapproximately 570-800 nm with the key wavelength for red in that range.As shown in FIG. 2B, a yellow filter element responds strongly to bothgreen light and red light, e.g., having a stronger response than theblue filter for the range approximately 500-800 nm and having a muchstronger response from 540 nm and longer wavelengths. These keywavelength values and wavelength ranges, as well as the charts shown inFIGS. 2A and 2B, are provided as examples. The techniques in theapplication are not limited to these examples and can be appropriatelyused with other wavelength ranges and filter response types.

The pixel 110 can be arranged as a two-by-two grid of filter elements(e.g., different filter regions), with yellow filter elements taking theplace of green filter elements of a Bayer pixel 100. For example, thetwo yellow filter elements can be located diagonally across from eachother rather than arranged side by side. In the pixel 110, a greenfilter element takes the place of the red filter element in the Bayerpixel 100. In general, the pixel 110 can represent a modified version ofa Bayer pixel 100, in which the green filter elements have been replacedwith yellow filter elements, and the red filter element has beenreplaced with a green filter element. The blue filter element remains,e.g., transmits blue light while substantially blocking red and greenlight.

In the Bayer pixel 100, green light is observed by 2 photosites. In thepixel 110, green light is observed by three photosites, which provides a50% sensitivity improvement for green light. In the Bayer pixel 100, redlight is observed by 1 photosite. In the pixel 110, red light isobserved by two photosites, which provides a 100% sensitivityimprovement for red light. The increase in the amount of light capturedby the pixel 110 may significantly reduce image noise and/or increaseimage resolution.

The arrangement of the filter elements of the enhanced color filterarray can produce a more natural looking noise profile in raw imagedata. Much of the noise in an image results from the measurementprocess. By capturing yellow light, e.g., both green and red light, atregions of the pixel 110, the resulting image can operate in a mannermore similar to the way the human eye perceives light. The arrangementshown in the pixel 110 can achieve these benefits with minimal change tomanufacturing techniques, e.g., allowing the same equipment andmanufacturing techniques used for Bayer sensors to minimize cost. Asnoted above, a first step toward biologically compatible sensitivity isto replace a Bayer filter's green elements with yellow elements, andreplace the Bayer filter's red elements with green elements.

The human eye includes cones that each detect one of three spectra: bluelight, a first range of yellow-green light, and a second range of yellowgreen light. The arrangement of filter elements in the pixel 110 modelsthis sensitivity better than a Bayer filter.

As an additional advantage of the enhanced color filter of the pixel110, the character of noise can be more pleasing than withBayer-filtered pixels. In general, noise characteristics can be morecompatible with human visual perception. For example, noise tends towardgreen and yellow. By contrast, noise for traditional Bayer-filteredpixels often provides pixels that are strongly green or red and can bedistracting. Often, the red pixels are most distracting and unnatural.In the enhanced color filter of the pixel 110, the most dominant noiseperceived will be yellow, which is consistent with human visualperception and less likely to distract a viewer. In other words, humanperception is accustomed to seeing the yellow noise, due to the mannerin which human cones in the eye are structured.

The color filter array with repeating elements of pixel 110 does notinclude any red filter elements (e.g., transmitting red light), or anymagenta elements (e.g., transmitting red and blue light). Nevertheless,the intensity of red light can be determined by subtracting the greenintensity from the yellow intensity (e.g., an average of the twoyellow-filtered regions).

In general, when subtracting one color channel from another, the effectadds noise sources (e.g., the subtraction result includes noise fromboth channels). The result is an increase in blurred signal-to-noiseratio (BSNR) for the red channel, with the red intensity having noiseincreased by a factor of the square root of two. However, when a personlooks at the resulting image data, it will be processed through thehuman visual system's yellow receptor screens, which can perform theinverse of the operation. As a result, the increase in red channel BSNRis reduced by the visual processing of the observer, and overall theobserver perceives less noise with the enhanced pixel 110 than the pixel100. Although the processing of an imaging device may increase noise bysubtracting green from yellow to infer red values, the observer will ineffect add the green and yellow together again when viewing the image.

With the color filter array using pixel 110, compared to theBayer-filtered pixel 100, luminosity will have less noise, but colornoise may increase. The noise may vary depending on the color space. Inthe RGB color space, the results from the pixel 110 would have more redchannel noise. Although there is increased sensitivity on capture of redlight, the subtraction of green from yellow to infer the red intensityincreases noise.

In some implementations, other color errors may result. For example,colors may not be co-located, chromatic aberrations of optics may beexacerbated, and high-frequency details at the pixel level or sub-pixellevel may cause false color or unnatural results. A camera or computingsystem can use a number of techniques to address these issues, such asoptical low-pass filtering when capturing images, or computationaltechniques such as the application of predictive algorithms or adjustingvalues based on surrounding pixels.

In the pixel 110, it can be advantageous to place the yellow-filteredelements where the green filter elements are located in a Bayer filter.Yellow intensity can be used as a proxy for luminosity. A processor of acamera or computing system can measure pixel luminosity using the yellowintensity signals generated by a sensor. The processor can thendetermine red and green color intensities using green-filtered regions,which are surrounded by four yellow-filtered regions each. Green andblue intensities can be determined directly from the image sensorregions corresponding to those filter elements. Then, an average can bedetermined for signals from two yellow-filtered regions adjacent agreen-filtered region, or even for all four yellow-filtered regionsadjacent the green-filtered region. The green intensity is thensubtracted from the average yellow intensity to determine a redintensity.

One or more hardware data processors can be used to perform imageprocessing. In some implementations, the color filter array is used withan imaging sensor having on the order of 10 million photosensitiveregions or cells, or 50 million photosensitive regions or cells, ormore. Further the system can be designed to be capable of capturingimages at 60 frames per second or more.

A camera or other device can store image data generated by an imagesensor with the color filter array having pixels 110 in a color spacethat matches the color filter elements. For example, the color space canrepresents images through three separate intensity channels for blue,yellow, and green (BYG). One example, is the LMS color space, whichrepresents images through three intensity channels that generallycorrespond to color characteristics detected by the human eye, e.g.,“long” cones sensitive to yellow light, “medium” cones sensitive togreen light, and “short” cones sensitive to blue light. Although humanvision may not exactly align to the color filter array (e.g., the longand medium cones both represent more of a yellow-green colors, ratherthan separate yellow and green elements), the representation can providea computationally efficient and space efficient manner of storing theimage data. Indeed, images can be stored in a compression format thatmodels blue, yellow, and green intensities and their correlations andcan provide a more efficient and effective compression process.

Though the color filter array does not include any pure red filterelements or even magenta filter elements (e.g., transmitting red andblue), the color filter array can nevertheless be used to provide a fullrange of colors (e.g., red, orange, yellow, green, blue, violet, etc.),whether or not in a color space that has a specific red color channel.In some implementations, the image data generated using the color filterarray and a corresponding image sensor can have a color gamut thatincludes at least the sRGB color space or the Adobe RGB color space, orany other appropriate color space representing visible color.

Variations of the color filter array may be made. In someimplementations, one of the yellow filter elements of the pixel 110 canbe replaced by a clear element to pass white (e.g., unfiltered) light,so that the repeating 2×2 grid includes yellow, white, green and bluefilter elements. This would provide a second sample of blue light in thepixel 110 and a further increase in overall sensitivity. This mayprovide decreased noise and/or an increase in spatial resolution.

In some implementations, the repeating pattern may be a pattern largerthan a 2×2 grid. For example, a 4×4 grid of element can be used, inwhich there is a more balanced mix of green and yellow across the grid.The same 2:1 ratio of yellow filter elements to green filter elementscan be used, but with a different arrangement of those elements. Thearrangement can be such that the 4×4 grid is itself not composed of arepeating 2×2 array. Better distribution, e.g., more even distributionover a larger area may increase the resulting color accuracy of theimage data.

Because the RGB color space is so common and standardized, other typesof color filters and other color spaces are typically not pursued. Theprocess of storing images in RGB involves Gamma compression mapping foreach color channel. This process is very different from the processingthat the human perception system uses for data generated by the eye, andit is difficult to obtain a good response for red colors. Reds andmagentas can be far off using Gamma correction toward the red channel.In human vision, gamma correction is instead effectively done for yellowand green and so storing and processing images in a BYG color space canprovide improvements.

Some approaches have represented images using YUV, where the U and Velements are quantized. Often, the most color information is describedby the U and V components, but quantization and other issues limit thecolor accuracy compared to a direct BYG approach.

FIG. 2A illustrates a graph 200 of example filter responsecharacteristics for elements of a Bayer color filter array.

FIG. 2B illustrates a graph 210 of example filter responsecharacteristics for an enhanced color filter array. For example, thegraph 210 show filter responses for blue, yellow, and green filterelements.

FIG. 3 illustrates an example of an imaging device 300 using an enhancedcolor filter array 320. The imaging device includes one or more lenses310, a color filter array 320, an image sensor 330, one or moreprocessors 340, and one or more data storage devices 350.

A color filter array 320 having an array of pixels 110 can be used inmany different types of cameras and other devices. For example, thecolor filter array 320 can be used in imaging modules for a mobilephone, a tablet computer, a compact camera, a mirrorless interchangeablelens camera, a digital single lens reflex camera, a security camera, amedical imaging device, and so on. The camera may be used for videocapture as well as still image capture.

The color filter array 320 has a repeating pattern of color filterelements, e.g., arranged as shown for the pixel 110 of FIG. 1B, wherethe color filter elements including yellow filter elements, green filterelements, and blue filter elements. In some implementations, the colorfilter elements do not include any red filter elements (e.g.,substantially transmitting red light while substantially blocking blueand green light) or magenta filter elements (e.g., filtered to transmitblue and red light while substantially blocking green light).

The imaging sensor 330 includes an array of separate photosensitiveregions 332. These regions can be sub-pixel regions, e.g., with fourphotosensitive regions providing data representing one pixel of outputimage data. The color filter array 320 can be aligned with the imagingsensor 330 so that each photosensitive region receives light filtered bya single color filter element of the color filter array 320. Lightpassing through the one or more lenses 310 reaches the color filterarray 320 so that incoming light to any given photosensitive region ofthe imaging sensor 330 is filtered by the corresponding color filterelement for the photosensitive region.

The imaging sensor 330 generates electrical signals indicating theintensity of light at each of the photosensitive regions. Theseelectrical signals are converted to digital form with ananalog-to-digital converter (ADC), and the digital signals are providedto the one or more processors 340. The one or more processors 340generate image data in an appropriate color space, e.g., in a BYG colorspace, a LMS color space, or an RGB color space. The one or moreprocessors 340 may generate RGB image data by, for example, subtractinggreen intensity measured for a pixel from the average yellow intensitymeasured for the pixel. The one or more processors 340 store the imagedata in the one or more data storage devices 350, which may includeflash memory or another type of data storage device.

In some implementations, the imaging device 300 operates using one ormore of the following functions. The imaging device 300 receives lightthrough the one or more lenses 310 and filters the received light withthe color filter array 320. Color-filtered light from the color filterelements of the color filter array 330 is received by and detected bydifferent photosensitive regions of the image sensor 330. The imagingdevice 300 produces signals indicating the intensities of light detectedat the different photosensitive regions of the image sensor 330, andgenerates image data for a color image (e.g., a two-dimensional array ofpixels) from the signals. The imaging device 330 then stores the imagedata in one or more data storage devices, such as internal or removablememory of the imaging device 330. The image data may specify the imageelements in any of various data formats or color spaces. For example,the image data may store the data as intensities, for each pixel, forblue, yellow, and green light, e.g., in a BYG color space or LMS colorspace. As another example, the image data may be stored in an RGB colorspace, with the imaging device 300 determining the red intensity foreach pixel based on subtracting a measure of detected green light from ameasure of detected yellow light. One or more processors of the imagingdevice 300 may use appropriate de-arraying algorithms to generate thepixel values for the image data, e.g., to perform color filter arrayinterpolation or color reconstruction.

Embodiments of the invention and all of the functional operationsdescribed in this specification may be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this specification and their structuralequivalents, or in combinations of one or more of them. Embodiments ofthe invention may be implemented as one or more computer programproducts, i.e., one or more modules of computer program instructionsencoded on a computer-readable medium for execution by, or to controlthe operation of, data processing apparatus. The computer readablemedium may be a non-transitory computer readable storage medium, amachine-readable storage device, a machine-readable storage substrate, amemory device, a composition of matter effecting a machine-readablepropagated signal, or a combination of one or more of them. The term“data processing apparatus” encompasses all apparatus, devices, andmachines for processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Theapparatus may include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal thatis generated to encode information for transmission to suitable receiverapparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) may be written in any form of programminglanguage, including compiled or interpreted languages, and it may bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program may be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programmay be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification may beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows may also be performedby, and apparatus may also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Moreover, a computer may be embedded inanother device, e.g., a tablet computer, a mobile telephone, a personaldigital assistant (PDA), a mobile audio player, a Global PositioningSystem (GPS) receiver, to name just a few. Computer readable mediasuitable for storing computer program instructions and data include allforms of non-volatile memory, media, and memory devices, including byway of example semiconductor memory devices, e.g., EPROM, EEPROM, andflash memory devices; magnetic disks, e.g., internal hard disks orremovable disks; magneto optical disks; and CD ROM and DVD-ROM disks.The processor and the memory may be supplemented by, or incorporated in,special purpose logic circuitry.

To provide for interaction with a user, embodiments of the invention maybe implemented on a computer having a display device, e.g., a CRT(cathode ray tube) or LCD (liquid crystal display) monitor, fordisplaying information to the user and a keyboard and a pointing device,e.g., a mouse or a trackball, by which the user may provide input to thecomputer. Other kinds of devices may be used to provide for interactionwith a user as well; for example, feedback provided to the user may beany form of sensory feedback, e.g., visual feedback, auditory feedback,or tactile feedback; and input from the user may be received in anyform, including acoustic, speech, or tactile input.

Embodiments of the invention may be implemented in a computing systemthat includes a back end component, e.g., as a data server, or thatincludes a middleware component, e.g., an application server, or thatincludes a front end component, e.g., a client computer having agraphical user interface or a Web browser through which a user mayinteract with an implementation of the invention, or any combination ofone or more such back end, middleware, or front end components. Thecomponents of the system may be interconnected by any form or medium ofdigital data communication, e.g., a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), e.g., the Internet.

The computing system may include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis specification in the context of separate embodiments may also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment mayalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination may in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments, and it should beunderstood that the described program components and systems maygenerally be integrated together in a single software product orpackaged into multiple software products.

In each instance where an HTML file is mentioned, other file types orformats may be substituted. For instance, an HTML file may be replacedby an XML, JSON, plain text, or other types of files. Moreover, where atable or hash table is mentioned, other data structures (such asspreadsheets, relational databases, or structured files) may be used.

Thus, particular embodiments of the invention have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims may be performed in a different orderand still achieve desirable results.

What is claimed is:
 1. An imaging device comprising: a color filterarray arranged to filter incident light, the color filter array having arepeating pattern of color filter elements, the color filter elementsincluding yellow filter elements, green filter elements, and blue filterelements; an image sensor having photosensitive regions corresponding tothe color filter elements, the photosensitive regions being configuredto respectively generate electrical signals indicative of intensity ofthe color-filtered light at the photosensitive regions; and one or moreprocessors configured to generate color image data based on theelectrical signals from the photosensitive regions and determine a redintensity for a pixel of the image data based on a green intensity of afirst photosensitive region corresponding to a particular green filterelement of the green filter elements and an average of yellowintensities of a second photosensitive region and a third photosensitiveregion corresponding to two particular yellow filter elements of theyellow filter elements, where the first, second, and thirdphotosensitive regions are adjacent to each other.
 2. The imaging deviceof claim 1, wherein green light is admitted through 75% of the colorfilter elements.
 3. The imaging device of claim 1, wherein the ratio ofyellow filter elements to green filter elements to blue filter elementsis 2:1:1.
 4. The imaging device of claim 1, wherein the one or moreprocessors are configured to provide image data indicating an array ofpixels, wherein each pixel is based on electrical signals from at leastone photosensitive region corresponding to a yellow color filterelement, at least one photosensitive region corresponding to a greencolor filter element, and at least one photosensitive regioncorresponding to a blue color filter element.
 5. The imaging device ofclaim 1, wherein the color filter elements do not include any red colorfilter elements or magenta color filter elements.
 6. The imaging deviceof claim 1, wherein an area of the color filter array that is comprisedof yellow filter elements is at least 50% of the average per-pixelcolor-filtered area of the color filter array.
 7. The imaging device ofclaim 1, wherein 75% of the color filter elements substantially transmitgreen light, and only 25% of the color filter elements filter incidentlight to substantially transmit only green light.
 8. The imaging deviceof claim 7, wherein 50% of the color filter elements substantiallytransmit red light, and none of the color filter elements filterincident light to substantially transmit only red light.
 9. The imagingdevice of claim 1, wherein the repeating pattern comprises a grid with arepeating 2 by 2 pattern of color filter elements, and wherein eachpixel of image data output by the imaging device is based on electricalsignals from four photosensitive regions respectively filtered by fourcolor filter elements, the four color filter elements including twoyellow filter elements, one blue filter element, and one green filterelement.
 10. The imaging device of claim 9, wherein the two yellowfilter elements are arranged diagonally across from each other in thegrid, and the blue filter element and the green filter element arearranged diagonally across from each other in the grid.
 11. The imagingdevice of claim 1, wherein the one or more processors are configured toprovide image data having a color gamut that includes at least the sRGBcolor space or the Adobe RGB color space.
 12. The imaging device ofclaim 1, wherein the one or more processors are configured to determinea red intensity for pixels of the image data by subtracting a greenintensity from a yellow intensity.
 13. The imaging device of claim 1,wherein the one or more processors are configured to provide the imagedata in values for a blue, yellow, and green color space or an LMS colorspace.
 14. The imaging device of claim 1, wherein the one or moreprocessors are configured to generate a compressed version of the imagedata that has a compressed form of data representing intensities ofblue, yellow, and green color channels.
 15. The imaging device of claim1, wherein the color filter array comprises wherein the repeatingpattern comprises a grid with a repeating 4 by 4 pattern of color filterelements.
 16. The imaging device of claim 1, wherein the image sensor isa CMOS sensor.
 17. The imaging device of claim 1, wherein the imagesensor is a CCD sensor.
 18. The imaging device of claim 1, wherein theimaging device is a mobile phone.
 19. The imaging device claim 1,wherein the repeating pattern comprises a repeating two by two patternof four color filter elements including two yellow filter elements, oneblue filter element, and one green filter element.
 20. An imaging devicecomprising: a color filter array arranged to filter incident light, thecolor filter array having a repeating pattern of color filter elements,the color filter elements including yellow filter elements, green filterelements, and blue filter elements; an image sensor havingphotosensitive regions corresponding to the color filter elements, thephotosensitive regions being configured to respectively generateelectrical signals indicative of intensity of the color-filtered lightat the photosensitive regions; and one or more processors configured togenerate color image data based on the electrical signals from thephotosensitive regions and determine a red intensity for a pixel of theimage data based on a green intensity of a first photosensitive regioncorresponding to a particular green filter element of the green filterelements and four yellow intensities of photosensitive regionscorresponding to four particular yellow filter elements of the yellowfilter elements, where the first photosensitive region is adjacent tothe four photosensitive regions.